Input receivers, like any semiconductor devices, undergo testing after the devices have been manufactured but before the shipment of the devices to distributors and customers. The ever increasing demand in speed and performance of integrated circuits requires high speed input receivers to respond and communicate with an input signal with a pulse width of less than 2 nanoseconds. The fast 2 nanosecond response time in pulse width makes the input receivers susceptible to signal glitches.
Reliability screening of semiconductor devices typically occurs at manufacturing sites to ensure the proper operation of the device over the stated lifetime of the product. Common characteristics of burn-in tests place semiconductor devices in a high temperature and a high voltage environment at long timing cycles and long signal rise and fall times. The high voltages also cause high currents to be drawn from the devices. The burn-in boards are also designed to fit as many devices as possible. These factors can contribute to noise being injected on the signal lines. The adverse testing environment in which input receivers are placed under during the burn-in test, in combination with noise signals being injected around the receiver switch point, can cause an input receiver to switch multiple times within a cycle. Multiple numbers of signal switching can cause an input receiver to change several times and place the device into an unknown state.
FIG. 1 is a waveform diagram that shows an input signal that would likely to cause an input receiver to glitch during a transition. As shown in FIG. 1, the input signal changes from a low state, to a high state, back to a low state across the switching point. The switching, or trip, point represents the threshold in which an input signal is considered to be a logic high signal or a logic low signal. The input signal in this waveform diagram entered into three different states by crossing the switching point twice, from a low to a high and then from a high to a low and then back to a high. Such instability of the signal transition in input signals can place a device into an unknown state and render the burn-in test results invalid or can cause device damage due to the unknown device state.
Accordingly, it is desirable to have an input receiver that slows the response to the fluctuation of input signals to minimize signal glitches.